5 Best Swap APIs for Web3 Wallet Developers

Web3 wallets are no longer just key managers. They are execution layers. The Web3 wallet market is projected to reach $8.93 billion in 2026, up from $6.57 billion in 2025 -- a 27.6% CAGR driven largely by in-wallet swap features. MetaMask alone generates $53.5 million annually from swap fees, Phantom's swap volume exceeded $20 billion in 2025, and DEX aggregators now route over $13.5 billion in daily trading volume across hundreds of liquidity pools.

For wallet developers, the swap API you integrate determines your chain coverage, your time-to-market, and whether your users see a "swap" button or a "swap on 3 chains" button. This guide compares the 5 best swap APIs for Web3 wallet development in 2026 -- ranked by what wallet developers actually care about: latency, transaction-ready calldata, multi-chain support, and integration friction.

What Wallet Developers Need From a Swap API

Before the comparison, here is the checklist that separates a usable swap API from a research project:

• Transaction-ready calldata: The API must return to, data, and value fields that can be passed directly to a wallet signer. If you need a second call to build the transaction, that is latency your users feel.
• Multi-chain support: With 30 million MetaMask monthly active users spread across Ethereum, Arbitrum, Base, Polygon, and BSC, a wallet that only swaps on one chain is leaving money on the table.
• No API key for development: Registration gates slow down prototyping. The best developer experience starts with a curl command, not a signup form.
• Slippage and partial fill handling: Wallets must protect users from MEV and low-liquidity pairs. The API should return minAmountOut and handle partial fills without crashing.
• RPC endpoints included: Wallet developers who support 10+ chains do not want to maintain their own RPC list. Bundled RPCs reduce infrastructure overhead.

1. Swap API (swapapi.dev)

Swap API is a free DEX aggregator API built for the wallet integration use case. It returns executable swap calldata from a single GET request across 46 EVM chains -- from Ethereum and Arbitrum to newer networks like Monad, MegaETH, Berachain, and Sonic. No API key, no registration, no payment.

The integration is a single HTTP call. Send chainId, tokenIn, tokenOut, amount, and sender, and get back a complete transaction object ready for signing:

curl "https://api.swapapi.dev/v1/swap/42161?tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&tokenOut=0xaf88d065e77c8cC2239327C5EDb3A432268e5831&amount=1000000000000000000&sender=0xYourWalletAddress"

The response includes expectedAmountOut, minAmountOut (with built-in slippage protection), priceImpact, full token metadata, and an array of up to 5 ranked RPC endpoints for the target chain. The tx object contains from, to, data, value, and gasPrice -- everything a wallet needs to present a confirmation screen and submit on-chain.

Swap API also handles edge cases that break wallet UIs in production. A Partial status returns adjusted amounts and an executable transaction for the available liquidity instead of failing. A NoRoute status returns cleanly so the wallet can show "pair not available" rather than a cryptic error. The envelope response format ({ success, data, error, timestamp }) is consistent across all status codes.

Why wallet developers pick it: 46 chains from one endpoint, zero setup, transaction-ready responses, and built-in RPC fallback lists. The rate limit is approximately 30 requests per minute per IP -- sufficient for wallet-scale usage without needing a billing account.

2. 1inch Swap API

1inch is the dominant DEX aggregator by volume, capturing over 59% of EVM DEX aggregator volume in Q2 2025. The Pathfinder algorithm splits trades across 400+ liquidity sources and claims up to 6.5% gas savings compared to single-DEX routes.

The 1inch Swap API v6 requires registration and an API key. Plans start with a free Dev tier (100,000 calls/month) and scale to $599/month for 7 million calls:

curl -H "Authorization: Bearer YOUR_API_KEY" "https://api.1inch.dev/swap/v6.0/1/swap?src=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&dst=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&from=0xYourWalletAddress"

The API covers 12 major blockchains. For wallet developers, the trade-off is clear: better routing depth on major chains, but narrower chain coverage and an API key requirement that adds friction during development. The free tier's 100,000 call limit can be tight for wallets with active user bases.

Best for: Production wallets focused on Ethereum, Arbitrum, and BSC where routing optimization on high-liquidity pairs is the priority over chain breadth.

3. 0x Swap API (Matcha)

The 0x API powers Matcha and provides swap infrastructure to dozens of wallets and dApps. Its differentiator is the RFQ (Request for Quote) system, which sources liquidity from professional market makers in addition to on-chain DEX pools. For large trades (over $10,000), RFQ quotes often beat pure on-chain routing.

0x requires an API key and moved to a paid model -- the free tier was discontinued in 2024. The API collects "Trade Surplus" (positive slippage) as its fee model:

curl -H "0x-api-key: YOUR_KEY" "https://api.0x.org/swap/v1/quote?buyToken=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&sellToken=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&sellAmount=1000000000000000000"

Chain support includes Ethereum, Polygon, BSC, Arbitrum, Optimism, Base, Avalanche, and several others. The API returns transaction-ready data, though the response schema differs from other aggregators, requiring some adapter logic in multi-provider wallet architectures.

Best for: Wallets handling large-value swaps where institutional-grade RFQ liquidity provides measurably better execution than on-chain routing alone.

4. Velora (formerly ParaSwap)

Velora, rebranded from ParaSwap in late 2025, has processed over $100 billion in historical volume. The API offers both REST endpoints and a JavaScript SDK, making it flexible for different wallet architectures.

Velora supports Ethereum, Polygon, BSC, Avalanche, Arbitrum, Optimism, Base, and Fantom. Its MultiPath routing algorithm splits trades across multiple DEXs and uses multi-hop paths for illiquid pairs. A separate buildTx endpoint constructs the transaction after you fetch a price quote:

curl "https://api.velora.xyz/prices?srcToken=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&destToken=0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48&amount=1000000000000000000&network=1"

The two-step flow (quote then build) adds latency compared to single-request APIs. For wallet developers, this means an extra round-trip before presenting the confirmation screen. Velora does offer a fee-sharing model (revenue share on swap fees), which can be attractive for wallets looking to monetize swaps.

Best for: Wallet teams that want a JavaScript SDK for complex frontend integrations and are willing to accept the two-step API flow.

5. LI.FI API

LI.FI is a DEX and bridge aggregation protocol. While other APIs on this list handle single-chain swaps, LI.FI combines swap routing with cross-chain bridging in a single request. If your wallet needs "swap ETH on Arbitrum to USDC on Base," LI.FI can route that in one call.

The API requires an API key (free tier available) and supports 30+ chains including both EVM and non-EVM networks:

curl -H "x-lifi-api-key: YOUR_KEY" "https://li.quest/v1/quote?fromChain=42161&toChain=8453&fromToken=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&toToken=0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913&fromAmount=1000000000000000000&fromAddress=0xYourAddress"

The trade-off for wallet developers: cross-chain capability comes with higher latency (bridge quotes are slower than single-chain swaps) and more complex response handling. For same-chain swaps, a dedicated aggregator API typically provides faster responses and simpler integration.

Best for: Wallets that need cross-chain swap functionality as a core feature and are willing to handle the added complexity of bridge routing.

Comparison Table

Feature	Swap API	1inch	0x	Velora	LI.FI
API Key Required	No	Yes	Yes	Yes	Yes
EVM Chains	46	12	~10	8	30+
Single-Request Tx	Yes	Yes	Yes	No (2-step)	Yes
Cross-Chain	No	No	No	No	Yes
Free Tier	Unlimited	100K calls/mo	No	Yes	Yes
RPC Endpoints Included	Yes (up to 5)	No	No	No	No
Partial Fill Handling	Yes	Limited	No	No	No
Response Format	Envelope	Flat JSON	Flat JSON	Flat JSON	Nested JSON

FAQ

What is the best swap API for Web3 wallet integration?

For most Web3 wallet developers, the best swap API is one that returns transaction-ready calldata in a single request without requiring an API key. Swap API (swapapi.dev) fits this criteria with 46 EVM chains, zero registration, and a response format that includes everything a wallet needs: the tx object for signing, expectedAmountOut for the confirmation screen, priceImpact for safety warnings, and rpcUrls for chain connectivity.

How do I add token swaps to my Web3 wallet?

Integrate a swap API that returns executable transaction data. Fetch a quote with the user's sender address, display expectedAmountOut and priceImpact on a confirmation screen, then submit the returned tx object through the wallet's signer. For ERC-20 input tokens, check the user's allowance first and prompt for approval if needed. Always run eth_estimateGas before submitting -- if it fails, the swap would revert on-chain.

Do swap APIs work across multiple blockchains?

Yes, but chain coverage varies significantly. Some APIs support 8-12 major chains while others cover 46 EVM networks from a single endpoint. For multi-chain wallets, look for an API where you only change the chainId parameter rather than switching base URLs or configuring separate endpoints per chain. This keeps your integration code simple as you add new networks.

How do I handle failed swaps in a wallet UI?

Check the API response status field before presenting the transaction. A Successful status means a full route was found. A Partial status means only part of the amount can be filled -- show the user the reduced amount and let them decide. A NoRoute status means no liquidity path exists -- display "swap unavailable for this pair" rather than a raw error. Always simulate the transaction with eth_call before submitting to catch balance, allowance, or deadline issues.

What slippage settings should wallets use for swap APIs?

A default maxSlippage of 0.005 (0.5%) works for most pairs on major chains. For low-liquidity tokens or newer chains, consider allowing users to adjust up to 1-3%. Check the priceImpact field in the response -- if it exceeds -5%, warn the user before proceeding. The minAmountOut field in the response reflects the on-chain minimum enforced by the smart contract, so the transaction will revert automatically if slippage exceeds the tolerance.

Get Started

Swap API is free, requires no API key, and supports 46 EVM chains. Start with a curl command and have swaps working in your wallet in minutes, not days.

• API base URL: https://api.swapapi.dev
• OpenAPI spec: https://swapapi.dev/openapi
• Documentation: https://swapapi.dev/llms.txt

curl "https://api.swapapi.dev/v1/swap/137?tokenIn=0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE&tokenOut=0x3c499c542cEF5E3811e1192ce70d8cC03d5c3359&amount=1000000000000000000&sender=0xYourWalletAddress"

No signup. No billing. Swap on Ethereum, Arbitrum, Polygon, Base, BSC, and 41 more chains from one endpoint.